An acoustic wave filter includes series arm resonators each including an IDT electrode on a piezoelectric substrate. Resonant frequencies of the series arm resonators are positioned within the pass band of the acoustic wave filter. The IDT electrode includes a pair of comb-shaped electrodes. Each of the comb-shaped electrodes includes electrode fingers and a busbar electrode. The electrode fingers extend in a direction intersecting a propagation direction of acoustic waves and are parallel with each other. One end of an electrode finger and one end of another electrode finger are connected with each other by the busbar electrode. The IDT electrode of the series arm resonator with the lowest anti-resonant frequency includes two or more withdrawal-weighted floating electrodes without any of the electrode fingers of one of the comb-shaped electrodes interposed therebetween.

An acoustic wave device includes a high-acoustic-velocity film, a piezoelectric layer provided directly or indirectly on the high-acoustic-velocity film, an IDT electrode provided on the piezoelectric layer, and a dielectric film provided on the piezoelectric layer to cover the IDT electrode. An acoustic velocity of bulk waves propagating through the high-acoustic-velocity film is higher than an acoustic velocity of acoustic waves propagating through the piezoelectric layer. The dielectric film includes a material including hydrogen atoms.

A first filter of a multiplexer includes serial resonators and parallel resonators that are acoustic wave resonators. A first of the serial resonators that is closer to a common terminal than the other serial resonators is connected to the common terminal without the parallel resonators interposed therebetween. Each of the elastic wave resonators includes a substrate having piezoelectricity, an IDT electrode provided on the substrate, and a dielectric layer provided on the substrate to cover the IDT electrode. A thickness of the dielectric layer of the first serial resonator is smaller than a thickness of each of the dielectric layers of the remainder of the elastic wave resonators.

An electroacoustic resonator (EAR) that allows an RF filter having a large bandwidth is provided. The resonator comprises a piezoelectric material (PM) and an electrode structure (ES, EF) on the piezoelectric material. The piezoelectric material is lithium niobate and has a crystal cut defined by the Euler angles (0°, 80° to 88°, 0°).

An acoustic wave filter includes a piezoelectric substrate, first and second input-output terminals, and a longitudinally coupled resonator unit in a path connecting the first and second input-output terminals to each other, and the resonator unit includes five or more interdigital transducer electrodes aligned in an acoustic wave propagation direction, the IDT electrodes include a center IDT electrode at the center in the propagation direction and first and second IDT electrodes at symmetric or substantially symmetric positions in the propagation direction with respect to the center IDT electrode, each of the first and second IDT electrodes includes a main pitch portion and a pair of narrow-pitch portions provided between the main pitch portion and both ends of the IDT electrode in the propagation direction, and the first and second IDT electrodes differ from each other in the number of electrode fingers of the main pitch portion.

An acoustic wave filter includes first and second series-arm resonators, each including an IDT electrode including electrode fingers and a busbar electrode connecting first ends of the electrode fingers to each other. A direction in which second ends of the electrode fingers are aligned with each other crosses a propagation direction of an acoustic wave. The electrode fingers of the IDT electrodes of the first and second series-arm resonators each include an electrode-finger central portion and a wide portion located at the second end and being wider than the electrode-finger central portion. The length of the wide portion of each of the electrode fingers in the first series-arm resonator is greater than the length of the wide portion of each of the electrode fingers in the second series-arm resonator.

An electronic device includes an insulation material layer provided on a first main surface of a piezoelectric substrate and surrounding a functional element, and a protective layer provided on the insulation material layer. The piezoelectric substrate and the insulation material layer define a hollow portion accommodating the functional element. The protective layer includes a first portion above the hollow portion, a second portion adjacent to the first portion at one end of the second portion, and a third portion adjacent to the second portion at another end of the second portion. A distance between the first main surface and a surface of the protective layer in the thickness direction is greatest at a location where the second portion is adjacent to or in a vicinity of the first portion, and the distance is shortest at a location where the second portion is adjacent to or in a vicinity of the third portion.

A first filter of a multiplexer includes serial resonators and parallel resonators that are acoustic wave resonators. A first of the serial resonators that is closer to a common terminal than the other serial resonators is connected to the common terminal without the parallel resonators interposed therebetween. Each of the elastic wave resonators includes a substrate having piezoelectricity, an IDT electrode provided on the substrate, and a dielectric layer provided on the substrate to cover the IDT electrode. A thickness of the dielectric layer of the first serial resonator is smaller than a thickness of each of the dielectric layers of the remainder of the elastic wave resonators.

A surface acoustic wave (SAW) device including a substrate is provided. Multiple surface acoustic wave elements are disposed on the substrate. A conductive surrounding structure includes: a wall part, disposed on the substrate and surrounding the surface acoustic wave elements; and a lateral layer part, disposed on the wall part. The lateral layer part has an opening above the surface acoustic wave elements. A cap layer covers the lateral layer part and closes the opening.

An electro-acoustic resonator comprises a piezoelectric substrate on which an electrode structure is disposed. The electrode structure comprises a metal layer of aluminum and copper, a barrier layer forming a barrier against the diffusion of copper and another metal layer disposed on the barrier layer comprising aluminum. An AlCu intermetallic phase formed after an anneal is restricted to the portion beneath the barrier layer so that Galvano-corrosion of the electrode structure is avoided.